Pneumatic tire and method of manufacturing the tire

ABSTRACT

A carcass  7  includes first and second carcass plies  9  and  10 . The first carcass ply  9  has a body portion  9 A extending from a tread portion  2  to a bead core  5  through a sidewall portion  3 , and a wound up portion  9 B which is folded back from inside to outside around the bead core  5 . The body portion  9 A is provided with the wound up portion  9 B. The second carcass ply  10  includes an inserting portion  10 B 2  which passes between a wound up portion  9 B and the body portion  9 A of the first carcass ply  9  from the tread portion  2  through the sidewall portion  3 . The inserting portion  10 B 2  enters a bead apex  6  and is terminated therein.

FIELD OF THE INVENTION

[0001] The present invention relates to a pneumatic tire having enhancedsteering stability, and a producing method thereof.

BACKGROUND ART

[0002] In recent years, with high performance tendency of automobiles,tires are required to have high steering stability and enhanced ridingcomfort, and it is required to reduce weight of tires in view ofresource conservation concerning environmental problem.

[0003] On the other hand, in the case of a pneumatic tire, especiallypneumatic radial tire, it is known that if lateral rigidity of the tireis increased, the steering stability can be enhanced. For this reason,in order to increase bending rigidity of a sidewall portion of the tire,there exists a so-called 1-1 structure in which a carcass comprises twocarcass plies, one of the carcass plies is wound up from inside tooutside of a bead core in an axial direction of the tire, and a lowerportion of the other carcass ply is wound down outside of a bead apex inthe tire axial direction.

[0004] According to this structure, since the two carcass plies sandwichthe bead apex, when bending deformation is applied to the bead portionof the tire by stress in the tire axial direction, compressive force isapplied to one of the carcass plies and tensile force is applied to theother carcass ply. Therefore, a neutral line of bending is located inthe bead apex which is made of hard rubber, and lateral bending rigidityis increased, and the steering stability is enhanced.

[0005] However, in the outer carcass ply in the tire axial directionwhich was wound down, conventionally, when a lower end edge of the wounddown portion is located at a tire radially outer side of the bead core,the lower portion is located outside of the wound up portion of thefirst carcass ply in the tire axial direction, or between the wound upportion and the bead apex.

[0006] In such a structure, however, the lower end edge of the wounddown carcass ply is prone to be close to a free end, and the lower endedge can not sufficiently endure the tensile force when bendingdeformation is applied to the bead portion, and the carcass ply can notcontribute to enhancement of lateral rigidity of the tire as comparedwith a carcass ply which is retained by the bead core.

[0007] If the wound down carcass ply is wound from tire radially inwardof the bead core to inner side in the tire axial direction and isretained, and a fixing strength at the bead portion is enhanced, it ispossible to enhance the lateral rigidity, but assembling of parts whentire is formed becomes difficult, productivity is lowered, and since thelength of the carcass ply is increased, a tire weight is also increased.

[0008] It is a well known technique to dispose, in the bead portion, areinforcing layer made of cord material having high rigidity such asmetal cord, thereby enhancing the bending rigidity of the tire, butincrease in tire weight can not be avoided, riding comfort isdeteriorated in generally, and there are many tires which do not havesuch reinforcing layer.

[0009] Japanese Patent Application Laid-open No. H6-344711 proposes astructure in which a wound down carcass ply is folded outside of thebead apex in the tire axial direction, thereby enhancing the rigidity ofthe bead portion. According to this proposed structure, the tire can bereduced in weight as compared with a tire using the reinforcing layer,the sandwiching pressure degree can be increased at the bead portion bythe folding and the fixing strength can be enhanced to some degree, butit is desired to further enhance the fixing strength.

DISCLOSURE OF THE INVENTION

[0010] Thereupon, based on a structure in which a lower portion of awound down carcass ply is disposed in a bead apex, it is an object ofthe present invention to provide a pneumatic tire in which a fixingstrength at the bead portion is increased to enhance the rigidity of thebead portion and lateral rigidity of the tire without deteriorating theriding comfort and increasing the tire weight. It is also an object ofthe invention to provide a producing method of such pneumatic tire.

[0011] A first invention of the present invention provides a pneumatictire having a carcass, in which the carcass comprises a first carcassply in which a body portion extending from a tread portion to a beadcore of a bead portion through a sidewall portion has a wound up portionwhich is folded back from inside to outside around the bead core, and asecond carcass ply passing between the body portion of the first carcassply and wound up portion from the tread portion through the sidewallportion, wherein

[0012] the wound up portion of the first carcass ply is disposed outsidein a tire axial direction of the bead apex which extends from the beadcore radially outward of the tire, the wound up portion extends radiallyoutward, a lower portion of the second carcass ply includes an insertingportion which enters in the bead apex and terminated therein, the lowerportion is continuously provided on the body portion which extends to abead apex upper end.

[0013] With this structure, at least a portion of the bead apex made ofhard rubber is sandwiched between the first and second carcass plies,and since the bead apex is strongly fixed, a tensile force is held, thelateral bending rigidity of the bead portion is enhanced, and steeringstability can be enhanced without increasing its weight. Since verticalrigidity of the tire can be maintained, almost no influence is generatedon riding comfort.

[0014] A second invention of the present invention provides a producingmethod of the pneumatic tire, the method comprises:

[0015] a first loading step for loading an inner liner, said firstcarcass ply, an inner bead apex portion forming an inside portion ofsaid bead apex in the tire axial direction, and said bead core on aformer,

[0016] a second loading step for loading said second carcass ply outsideof said inner bead apex portion, and

[0017] a covering step at least a portion of an outside portion of saidsecond carcass ply with an outer bead apex portion forming an outsideportion of said bead apex in the tire axial direction, and with a woundup portion of said first carcass ply which comes out from said bead corein the axial direction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a sectional view of a right half of a tire according toan embodiment of the present invention.

[0019]FIG. 2 is an enlarged sectional view of a bead portion of thetire.

[0020] FIGS. 3(a) to 3(c) are diagrams of forming steps of the beadportion.

[0021] FIGS. 4(a) and 4(b) are diagram showing another forming steps.

[0022]FIG. 5 is a sectional view showing another embodiment of the beadportion.

[0023]FIG. 6 is a sectional view showing further another embodiment ofthe bead portion.

BEST MODE FOR CARRYING OUT THE INVENTION

[0024] An embodiment of the present invention will be explained belowbased on the drawings.

[0025] In FIG. 1, a pneumatic tire 1 is assembled to a normal rim 8 anda normal internal pressure is charged into the tire, while taking thecase of a radial tire for a passenger car, but the pneumatic tire 1 canalso be applied to various tires such as a small truck tire, a trucktire and a motorcycle tire. In this specification, the “normal rim” isdetermined in accordance with any one of a standard rim defined byJATMA, a “Design Rim” defined by TRA, and a “Measuring Rim” defined byETRTO. The “normal internal pressure” is an air pressure defined by anyone of a maximum air pressure defined by JATMA, a maximum valuedescribed in a table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATIONPRESSURES” defined by TRA, and “INFLATION PRESSURE” defined by ETRTO.

[0026] The pneumatic tire 1 comprises a tread portion 2 forming a treadsurface, sidewall portions 3 on the opposite sides of the tread portion2, and bead portions 4 located radially inward of the sidewall portions3. A bead core 5 formed by spirally winding a metal wire several timesis disposed in the bead portion 4, and a bead apex 6 is disposedradially outside of the tire of the bead core 5.

[0027] The pneumatic tire 1 has a carcass 7. The carcass 7 comprises afirst carcass ply 9 in which a body portion 9A extending from the treadportion 2 to a bead core 5 of a bead portion 4 through a sidewallportion 3 is continuously provided with a wound up portion 9B which isfolded back from inside to outside in the tire axial direction aroundthe bead core 5, and a second carcass ply 10 disposed radially outwardof the tire with respect to the first carcass ply 9 and having a bodyportion 10A extending from the tread portion 2 to an upper end 6 a ofthe bead apex 6 through the sidewall portion 3 and the body portion 10Ais provided with a lower portion 10B. In this example, the secondcarcass ply 10 is of a 1-1 structure in which the second carcass ply 10is wound down between the body portion 9A and the wound up portion 9B ofthe first carcass ply. The number of first or second carcass ply (9 or10) may be two or more.

[0028] In the bead apex 6 of this example, a bead apex height H6 whichis a distance in the tire radial direction from an upper surface of thebead core 5 (from central point 5 c in the tire axial direction when theupper surface is inclined) to the upper end 6 a is set to a higher valuethan that of a normal tire as high as about 25 to 55% of a carcassheight H7 from the upper surface of the bead core 5 to a point of a tireequator surface C of an inner surface of the carcass 7.

[0029] Further, a height H9 from the upper surface of the bead core 5 toan upper end 9 a of the wound up portion 9B of the first carcass ply 9is set to about 30 to 60% of the carcass height H7. The wound up portion9B may extend below the tread portion 2 but generally, if the height H9exceeds 60%, a weight of the tire is increased, vertical rigidity isincreased, and riding comfort is prone to be deteriorated. Further, in aregion of tire maximum width position, a large bending stress is proneto be applied, and it is preferable locate the upper end 9 a of thewound up portion 9B in a region of 3% of the carcass height H7 aroundthis region and more preferably, 5% of the carcass height H7. If thisvalue is less than 25%, lateral rigidity of the bead portion 4 islowered, and steering stability is deteriorated.

[0030] Preferably, the height H9 to the upper end 9 a of the wound upportion 9B of the first carcass ply 9 is greater than the bead apexheight H6 by about 4 to 24% of the height H6. With this design, the bodyportion 9A and the wound up portion 9B are adjacent to each otherthrough the second carcass ply 10, this is of use in strongly holdingthe second carcass ply 10.

[0031] The bead apex 6 is made of hard rubber having durometer Ahardness of 75 to 95°. The sidewall rubber of the sidewall portion 3 ismade of rubber having hardness of 50 to 60°. In this specification, thehardness means durometer A hardness, and is defined as durometer type Abased on JIS-K6253.

[0032] In this embodiment, the lower portion 10B of the second carcassply 10 comprises a covering portion 10B1 which passes between the outerside surface of the bead apex 6 and the wound up portion 9B radiallyinward from the upper end 6 a of the bead apex 6, and an insertingportion 10B2 which is inserted into the bead apex 6 from an inlet aformed in a lower end of the covering portion 10B1 and is terminated. Aninserting height Ha of the inserting portion 10B2 from an upper surfaceof the bead core 5, i.e., inserting height Ha of the inlet a from theupper surface of the bead core 5 can be 0.2 to 1.0 times (preferablyabout 0.25 to 0.7 times) of the bead apex height H6. If the insertingheight Ha is smaller than 0.2 Ha, fixing effect at the bead apex 6 bythe inserting portion 10B2 is inferior. If this value is preferably setto about 0.25 to 0.7 times as described above, the fixing effect as wellas sandwiching effect of the bead apex 6 by the first and second carcassplies 9 and 10 can effectively be exhibited.

[0033] As shown in FIG. 2 in an enlarged manner, the inserting portion10B2 is inserted at substantially intermediate height of the bead apex 6as the inlet a, and a position of the end edge 10 a is located in arange from a tire axial direction central point 5 c of the bead core 5to a position away from the central point 5 c in the tire axialdirection by a distance of ¼ times (preferably ⅙ times) of a tire axialdirection length 5L, and preferably the position of the end edge 10 a islocated in the vicinity of the central point 5 c. With this design,fixing effect by the bead apex 6 can be enhanced.

[0034] In this embodiment, the end edge 10 a is in contact with an uppersurface of the bead core 5. With this design, the bead apex 6 is dividedinto an outer bead apex portion 6A and an inner bead apex portion 6B inthe tire axial direction, and the inserting portion 10B2 is fixed overthe entire height of the inserting height Ha. When the end edge heightH10 a (shown in FIG. 5) in the radial direction between the end edge 10a and the upper surface of the bead core 5 is set to about 0 to 0.2times of the bead apex height H6 and a gap is formed, the bead apex 6can integrally be formed inside and outside of the inserting portion10B2, which can contribute to enhancement of the rigidity. In theinserting portion 10B2, if a portion between the inlet a and the endedge 10 a is made straight and no looseness is generated, extensibilityat the time of tension is reduced, and the fixing effect can bemaintained or enhanced.

[0035] In the embodiment shown in FIG. 1, in the outer bead apex portion6A and the inner bead apex portion 6B, the outer bead apex portion 6A ismade of hard rubber having hardness of 85 to 95° for example, therebyenhancing the fixing strength of the second carcass ply 10, and thehardness of the inner bead apex portion 6B is set to 75 to 85°, so thatbending or deforming of the sidewall portion 3 is facilitated, therebyenhancing the riding comfort.

[0036] Each of the first carcass ply 9 and the second carcass ply 10 ofthe carcass 7 is made of organic fiber cord such as nylon, polyester,rayon and aromatic polyamide, and has carcass cords 10 c (shown in FIG.2) radially arranged in parallel to each other at an angle of 80 to 90°with respect to the tire equator CO. The carcass cords 10 c are lined upto form a cord parallel body, and this is embedded in a carcass toppingrubber layer 10 r, and the outer bead apex portion 6A and the inner beadapex portion 6B are coupled and fixed to each other through the carcasstopping rubber layer 10 r. The pneumatic tire 1 includes an inner liner13 disposed on a tire lumen surface and made of rubber such as butylrubber through which air can hardly pass, a belt layer 11 disposed onthe tread portion 2, and a band layer 12 superposed on the outer side ofthe belt layer 11. A chafer (not shown) for preventing deviation withrespect to the rim can be disposed on a contact surface of the beadportion 4 with respect to the rim 8.

[0037] The belt layer 11 is formed by superposing a plurality of (two,in this example) belt plies made of organic fiber cord such as nylon,rayon, aromatic polyamide fiber arranged at an angle of 15 to 35° withrespect to the tire equator CO, thereby enhancing the rigidity of thetread portion 2. The band layer 12 comprises one band ply covering theentire surface of the belt layer 11. The band layer 12 is formed byspirally winding a long and narrow band-like ply made of one or moreorganic fiber cords such as nylon, aromatic polyamide fiber coated withtopping rubber. High load resistance and endurance are enhanced bypreventing the lifting of the belt layer 11 at the time of high speedrunning, by enhancing high speed performance, and by preventing the beltlayer 11 from being peeled off.

[0038]FIG. 3 shows one example of a producing method of the pneumatictire 1 having the above-described bead portion structure.

[0039] (1) First Stage

[0040] As shown in FIG. 3(a), the inner liner 13, the first carcass ply9, the inner bead apex portion 6B and the bead core 5 are laminated on aformer 14 in this order (first loading step). Here, it is preferablethat the bead core 5 and the inner side of the inner bead apex portion6B are previously assembled to each other as a pair. Then, the secondcarcass ply 10 is mounted such that its end edge 10 a reaches the beadcore 5 (second loading step).

[0041] (2) Second Stage

[0042] As shown in FIG. 3(b), the outer bead apex portion 6A is placedon the second carcass ply 10 such that the bead apex portion 6A comesinto contact with the bead core 5. Then, as shown in FIG. 3(c), thefirst carcass ply 9 is wound around the bead core 5 to cover the outerbead apex portion 6A such that the upper end 9 a of the first carcassply 9 comes closer to a center of the former than the upper end 6 a ofthe bead apex portion 6B (covering step).

[0043] In this step, the inner and outer bead apex portions 6A and 6Bmay be made of the same material or different material.

[0044]FIG. 4 show an example of other steps.

[0045] (1) First Stage

[0046] As shown in FIG. 4(a), the inner liner 13, the first carcass ply9, the bead apex 6, the bead core 5 and the second carcass ply 10 areplaced on the former 14 in this order (first and second loading steps).Here, the rubber of the bead apex 6 is a rubber-molded product formed byconnecting the outer and inner bead apex portions 6A and 6B through athin joint portion 6C.

[0047] (2) Second Stage

[0048] As shown in FIG. 4(b), the first carcass ply 9 and the outer beadapex portion 6A are integrally wound up simultaneously, the outer beadapex portion 6A is formed, and the second carcass ply 10 is sandwichedbetween the outer and inner bead apex portions 6A and 6B (coveringstep).

[0049]FIG. 6 shows the bead portion of the pneumatic tire 1 produced bythe above steps. The bead apex 6 entirely made of the same rubber andfixing the second carcass ply 10 is formed around the bead core 5. Thisstep can prevent a dividing step of the bead apex 6.

[0050]FIG. 5 shows a case in which a second carcass ply end edge 10 a isformed by separating the same from an upper surface of the bead core 5by a height H10 a, and this can be formed by any steps shown in FIGS. 3and 4.

CONCRETE EXAMPLE

[0051] Tires having size of 205/55R16 and structure shown in FIG. 1 wereprototyped, and test concerning performance of the tires was carriedout. The tires were mounted to a Japanese passenger car, the car wasallowed to run on a test course, and a driver's sensory evaluation wasindicated with indices with 10 point scoring while defining acomparative example 1 as being 5. The higher the numerical value, moreexcellent the result is. Results of the test are shown in Table 1.Comparative Embodiment Embodiment Embodiment Embodiment Embodimentexample 1 1 2 3 4 5 Tire size 205/55R16 Drawing showing — structureInserting height Ha of 0 7 10 15 20 3 second carcass ply [mm] Height H6of bead apex 35 [mm] Ratio Ha/H6 0 0.2 0.28 0.42 0.57 0.08 Steeringstability 5 7 7 7 6 6 Riding comfort 5 5 5 5 5 5

[0052] In Table 1, the steering stability and riding comfort weremeasured in the following manner:

[0053] (1) Steering Stability

[0054] The test tires were mounted to four wheels of a Japanese FF car,the car was allowed to run on a tire test course having dry asphalt roadsurface, characteristics concerning steering wheel response, rigidityfeeling, grip and the like were indicated with indices with driver'ssensory evaluation while defining the comparative example 1 as being100. The higher the numerical value, more excellent the result is.

[0055] (2) Riding Comfort

[0056] Like the above test, on bumps of dry asphalt roar surface,Belgian road (road surface stone pavement), Bitzmen road (pebble roadsurface) and the like, sensory evaluation concerning rhino-hide feeling,toss up and damping was carried out, results were indicated with indiceswhile defining the comparative example 1 as being 100. The higher thenumerical value, more excellent the result is.

[0057] As a result of the test, it was confirmed that tires of theembodiments were excellent in steering stability, and riding comfort wasnot inferior.

INDUSTRIAL APPLICABILITY

[0058] As explained above, according to the pneumatic tire of thepresent invention, it is possible to enhance the steering stabilitywhile maintaining the riding comfort, and the invention can bepreferably applied to various tires such as passenger car tires, smalltruck tires, truck tires and motorcycle tires.

1. A pneumatic tire having a carcass, in which the carcass comprises afirst carcass ply in which a body portion extending from a tread portionto a bead core of a bead portion through a sidewall portion has a woundup portion which is folded back from inside to outside around said beadcore, and a second carcass ply passing between said body portion of saidfirst carcass ply and wound up portion from the tread portion throughthe sidewall portion, wherein said wound up portion of said firstcarcass ply is disposed outside in a tire axial direction of the beadapex which extends from said bead core radially outward of the tire,said wound up portion extends radially outward, a lower portion of saidsecond carcass ply includes an inserting portion which enters in saidbead apex and terminated therein, said lower portion is continuouslyprovided on the body portion which extends to a bead apex upper end. 2.A pneumatic tire according to claim 1, wherein the lower portion of saidsecond carcass ply comprises a covering portion which extends from a tipend of said bead apex along the tire axial direction of said bead apex,and said inserting portion which enters in said bead apex from a lowerend of said covering portion and is terminated in said bead apex.
 3. Apneumatic tire according to claim 1 or 2, wherein an inserting height Haof said inserting portion from an upper surface of said bead core is 0.2to 1.0 times of a height H6 of said bead apex.
 4. A pneumatic tireaccording to any one of claims 1 to 3, wherein a height H10 a of an endedge of said lower portion between itself and an upper surface of saidbead core in the radial direction is 0 to 0.2 times of a height H6 ofsaid bead apex, and a position of said end edge in the tire axialdirection is in a range from a tire axial direction central point ofsaid bead core to a position away from the central point in the tireaxial direction by a distance of ¼ times of a tire axial directionlength.
 5. A producing method of a pneumatic tire having a first carcassply in which a body portion extending from a tire pattern to a bead coreof a bead portion through a sidewall portion has a wound up portionwhich is folded back from inside to outside around said bead core, and asecond carcass ply passing between said body portion of said firstcarcass ply and wound up portion from the tread portion through thesidewall portion, the second carcass ply having an inserting portionwhich enters the bead apex and terminated therein, wherein said methodcomprises: a first loading step for loading an inner liner, said firstcarcass ply, an inner bead apex portion forming an inside portion ofsaid bead apex in the tire axial direction, and said bead core on aformer, a second loading step for loading said second carcass plyoutside of said inner bead apex portion, and a covering step at least aportion of an outside portion of said second carcass ply with an outerbead apex portion forming an outside portion of said bead apex in thetire axial direction, and with a wound up portion of said first carcassply which comes out from said bead core in the axial direction.
 6. Aproducing method of a pneumatic tire according to claim 5, wherein insaid covering step, after said outer bead apex portion is placed on theat least a portion of the outside portion of said second carcass ply,the wound up portion of said first carcass ply is wound up.
 7. Aproducing method of a pneumatic tire according to claim 5, wherein insaid first loading step, an inner bead apex rubber portion which isconnected to the outer bead apex portion located on said wound upportion through a joint portion passing inside said bead core is used,In said covering step, the wound up portion of said first carcass ply iswound up, and said outer bead apex portion is disposed outside of saidsecond carcass ply.